Abstract
This work aimed to study the comprehensive effects of photo-oxidation and biodegradation on different failure stages of polyester coatings,which were exposed to the tropical rainforest atmosphere.The surface morphology,aging products,local aging characteristics and electrochemical behavior of the coatings were characterized with scanning electron microscope (SEM),fourier transform infrared spectroscopy (FTIR),electrochemical impedance spectroscopy (EIS) and high-resolution dispersive Raman microscope.The results showed that the surface of coatings became rougher and fungal hyphae distributed more densely on surface with the increasing of exposure time.From the aspect of polymer structure,the ultraviolet radiation destroyed the main chain of polyester through the photo-oxidation process,resulting in the breakage of aliphatic ester bonds and the formation of esters.Further,the metabolites of fungi can promote the hydrolysis of oligomers produced by the photo-oxidation.In a short,the photo-oxidation could facilitate the biodegradation of the coating.With the synergistic effect of UV photo-oxidation and fungal biodegradation,a rapid diffusion tunnel between the coating surface and the metal substrate was established at the pore defects of the coating,which finally accelerated the corrosion failure process of the coating.The main corrosion products include α-Fe2O3,ZnO and Zn5(OH)6(CO3)2.
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